Electronic device with switched-capacitor tuning and related method

ABSTRACT

An electronic device includes an inductive element, and variable capacitors. Each variable capacitor includes: first and third capacitors, both having a first terminal electrically connected to a first terminal of the inductive element; and second and fourth capacitors, both having a first terminal electrically connected to a second terminal of the inductive element. A first switch circuit electrically connects or isolates a second terminal of the first capacitor to/from a second terminal of the second capacitor. A second switch circuit electrically connects or isolates a second terminal of the third capacitor to/from a second terminal of the fourth capacitor. A third switch circuit electrically connects or isolates the second terminal of the first capacitor to/from the second terminal of the fourth capacitor. A fourth switch circuit electrically connects or isolates the second terminal of the third capacitor to/from the second terminal of the second capacitor.

This application claims priority to U.S. Provisional Application Ser.No. 61/748,681, filed on Jan. 3, 2013, entitled “Electronic Device withSwitched-Capacitor Tuning and Related Method,” which application ishereby incorporated herein by reference.

BACKGROUND

The semiconductor industry has experienced rapid growth due toimprovements in the integration density of a variety of electroniccomponents (e.g., transistors, diodes, resistors, capacitors, etc.). Forthe most part, this improvement in integration density has come fromshrinking the semiconductor process node (e.g., shrinking the processnode towards the sub-20 nm node). As device dimensions shrink, voltagenodes also shrink, with modern core device voltages trending toward lessthan 1 Volt, and input/output (I/O) device voltages under 2 Volts.

Many types of analog, digital and mixed-signal circuits rely on tuningnetworks to achieve fine granularity in performance metrics, such asgain, bandwidth, center frequency, oscillation frequency, and the like.The tuning networks are often designed with a view to increaseresolution while maintaining or shrinking area and also guarding againstprocess, voltage, and temperature (PVT) variation.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present embodiments, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a circuit diagram of an electronic device in accordance withvarious embodiments of the present disclosure;

FIG. 2 is a diagram of the variable capacitor network in accordance withvarious embodiments of the present disclosure;

FIG. 3 is a diagram of a variable capacitor in accordance with variousembodiments of the present disclosure;

FIG. 4 is a diagram of the variable capacitor having the firstcapacitance in accordance with various embodiments of the presentdisclosure;

FIG. 5 is a diagram of the variable capacitor having the secondcapacitance in accordance with various embodiments of the presentdisclosure;

FIGS. 6 and 7 are diagrams of switch circuits in accordance with variousembodiments of the present disclosure;

FIGS. 8, 9, 10 and 11 are diagrams of operating modes of the switchcircuits in accordance with various embodiments of the presentdisclosure;

FIG. 12 is a flowchart of a method of operating an electronic devicewith switched-capacitor tuning in accordance with various embodiments ofthe present disclosure;

FIG. 13 is a circuit diagram of a digitally-controlled oscillator (DCO)in accordance with various embodiments of the present disclosure; and

FIG. 14 is a flowchart of a method of designing an electronic devicewith switched-capacitor tuning in accordance with various embodiments ofthe present disclosure.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the present embodiments are discussed in detailbelow. It should be appreciated, however, that the present disclosureprovides many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative of specific ways to make and use the disclosedsubject matter, and do not limit the scope of the different embodiments.

Embodiments will be described with respect to a specific context, namelyan electronic circuit with switched-capacitor tuning, and the like.Other embodiments may also be applied, however, to other types ofanalog, digital, or mixed-signal circuits.

Throughout the various figures and discussion, like reference numbersrefer to like components. Also, although singular components may bedepicted throughout some of the figures, this is for simplicity ofillustration and ease of discussion. A person having ordinary skill inthe art will readily appreciate that such discussion and depiction canbe and usually is applicable for many components within a structure.

Analog, digital, and mixed-signal circuits are characterized by certainperformance metrics, such as gain, direct current (DC) offset,bandwidth, center frequency, oscillator frequency, resolution, noiserejection, power consumption, and the like. Nearly every type ofperformance metric is controllable through proper circuit design.Constraints on circuit area and power consumption can impose trade-offsbetween the performance metrics defined for a circuit, such as anamplifier, a filter, a phase-locked loop (PLL), an analog-to-digitalconverter (ADC), a digital-to-analog converter (DAC), or the like. Inmany applications, tuning networks are included either to fine-tune aperformance metric prior to shipping a final product, or to select anappropriate level for the performance metric on-the-fly. One example ofthe former would include a tunable bias circuit, such as a tunablecurrent mirror, that tunes a low noise amplifier (LNA) for noise figureor input-referred third-order intercept point (IIP3). An example of thelatter would be a variable capacitor used in an LC tank circuit fordigitally controlling oscillation frequency of the LC tank circuit.

In the following disclosure, a novel electronic device withswitched-capacitor tuning is introduced. The electronic device uses aswitched-capacitor variable capacitance network to improve performance(e.g., resolution, PVT variation) of a circuit of the electronic devicewhile maintaining low area. The circuit in conjunction with theswitched-capacitor variable capacitance network exhibits highresolution, precise capacitance, and small area.

FIG. 1 is a circuit diagram of an electronic device 10 in accordancewith various embodiments of the present disclosure. The electronicdevice 10 includes a circuit 100 and a variable capacitance network 110.In some embodiments, the circuit 100 has an input terminal for receivinga first signal S1, and an output terminal for outputting a second signalS2. In some embodiments, the variable capacitance network 110 has afirst terminal electrically connected to a first internal node of thecircuit 100, and a second terminal electrically connected to a secondinternal node of the circuit 100. In some embodiments, the firstterminal is an inverting output terminal, and the second terminal is anon-inverting output terminal.

The circuit 100 is an analog circuit, a digital circuit, a mixed-signalcircuit, a combination thereof, or the like. In some embodiments, thecircuit 100 is a digitally-controlled oscillator (DCO) used with anall-digital phase-locked loop (ADPLL). In some embodiments, the circuit100 is a filter. In some embodiments, the circuit 100 is a radiotransceiver, an amplitude modulator, an analog-to-digital converter(ADC), an impedance matching network, a programmable gain amplifier, orthe like.

FIG. 2 is a diagram of the variable capacitor network 110 in accordancewith various embodiments of the present disclosure. The variablecapacitor network 110 includes variable capacitors 111, 112, . . . , 113electrically connected in parallel. Number N of the variable capacitors111, 112, . . . , 113 is a positive integer. The variable capacitor 111is described as an example. In some embodiments, capacitance of thevariable capacitor 111 is switchable between a first capacitance and asecond capacitance. In some embodiments, the first capacitance is lessthan the second capacitance. A difference between the second capacitanceand the first capacitance is a capacitance delta (ΔC). In someembodiments, a single control signal is used to select the firstcapacitance or the second capacitance. The single control signal has atleast two states, e.g. logic high or logic low, binary one or binaryzero, on or off, or the like. In some embodiments, a first controlsignal and a second control signal are used to select the firstcapacitance or the second capacitance. The first control signal isinverse of the second control signal. When the first control signal islogic high, for example, the second control signal is logic low. Whenthe first control signal is logic low, the second control signal islogic high. Other variable capacitors 112, . . . , 113 are operatedsimilarly to the variable capacitor 111.

In some embodiments, first capacitances of the variable capacitors 111,112, . . . , 113 are different (e.g., binary code, gray code), andsecond capacitances of the variable capacitors 111, 112, . . . , 113 aredifferent (e.g., binary code, gray code). For example, the firstcapacitance of the variable capacitor 111 may be 16*C, and the firstcapacitance of the variable capacitor 112 may be 8*C, where C is a unitcapacitance. In some embodiments, the first capacitances of the variablecapacitors 111, 112, . . . , 113 are the same (e.g., thermometer code),and the second capacitances of the variable capacitors 111, 112, . . . ,113 are the same (e.g., thermometer code). In some embodiments, variablecapacitors representing upper bits (e.g., most significant bits (MSBs))of the variable capacitor network 110 have binary coded capacitances,and lower bits (e.g., least significant bits (LSBs)) of the variablecapacitor network 110 have thermometer coded capacitances. In someembodiments, the capacitance deltas (ΔC) of the variable capacitors 111,112, . . . , 113 are thermometer-coded, binary-coded, hybrid-coded, orthe like.

Total capacitance of the variable capacitor network 110 is equal to thesum of the individual capacitances of the variable capacitors 111, 112,. . . , 113. In some embodiments, a baseline capacitance C_(min) of thevariable capacitor network 110 is equal to the sum of the firstcapacitances of the variable capacitors 111, 112, . . . , 113. In someembodiments, a maximum capacitance C_(max) of the variable capacitornetwork 110 is equal to the sum of the second capacitances of thevariable capacitors 111, 112, . . . , 113. Resolution of the variablecapacitor network 110 is determined by number and type of bits of thevariable capacitors 111, 112, . . . , 113. For example, 64 discretecapacitances may be represented by 64 capacitor deltas having thethermal-coded capacitances (e.g., ΔC, ΔC, ΔC, . . . , ΔC), 6 capacitordeltas having binary-coded capacitances (e.g., 32*ΔC, 16*ΔC, 8*ΔC, 4*ΔC,2*ΔC, 1*ΔC), or 7 capacitor deltas having hybrid-coded (binary andthermal) capacitances (e.g., 32*ΔC, 16*ΔC, 8*ΔC, 4*ΔC, ΔC, ΔC, ΔC),where ΔC is a unit capacitance delta (e.g., 10 attofarads).

FIG. 3 is a diagram of a variable capacitor 311 in accordance withvarious embodiments of the present disclosure. The variable capacitor311 is an example of one type of variable capacitor that is used in someembodiments for the variable capacitors 111, 112, . . . , 113. A firstterminal of a first capacitor 121 is electrically connected to a node 31(e.g., a node OUT+ shown in FIG. 2). A second terminal of the firstcapacitor 121 is electrically connected to a node 11. The firstcapacitor 121 has a first capacitance CA (e.g., 1 femtofarad). A firstterminal of a second capacitor 122 is electrically connected to a node32 (e.g., a node OUT− shown in FIG. 2). A second terminal of the secondcapacitor 122 is electrically connected to a node 12. In someembodiments, the second capacitor 122 has the first capacitance CA. Insome embodiments, the second capacitor 122 has a different capacitancethan the first capacitor 121. A first switch 131 has a first terminalelectrically connected to the node 11. A second terminal of the firstswitch 131 is electrically connected to the node 12. In someembodiments, the first switch 131 is controllable by an electricalsignal. In some embodiments, the first switch 131 is an N-typemetal-oxide semiconductor (NMOS) transistor, a P-typemetal-oxide-semiconductor (PMOS) transistor, a pass gate, or the like.When the first switch 131 is closed (turned on, short-circuited), thesecond terminal of the first capacitor 121 is electrically connected tothe second terminal of the second capacitor 122. When the first switch131 is open (turned off, open-circuited), the second terminal of thefirst capacitor 121 is electrically isolated from the second terminal ofthe second capacitor 122.

A first terminal of a third capacitor 123 is electrically connected tothe node 31. A second terminal of the third capacitor 123 iselectrically connected to a node 13. The third capacitor 123 has asecond capacitance CB (e.g., 1.2 femtofarads). A first terminal of afourth capacitor 124 is electrically connected to a node 32. A secondterminal of the fourth capacitor 124 is electrically connected to a node14. In some embodiments, the fourth capacitor 124 has the secondcapacitance CB. In some embodiments, the fourth capacitor 124 has adifferent capacitance than the third capacitor 123. A second switch 132has a first terminal electrically connected to the node 13. A secondterminal of the second switch 132 is electrically connected to the node14. In some embodiments, the second switch 132 is controllable by anelectrical signal. In some embodiments, the second switch 132 is anN-type metal-oxide semiconductor (NMOS) transistor, a P-typemetal-oxide-semiconductor (PMOS) transistor, a pass gate, or the like.When the second switch 132 is closed (turned on, short-circuited), thesecond terminal of the third capacitor 123 is electrically connected tothe second terminal of the fourth capacitor 124. When the second switch132 is open (turned off, open-circuited), the second terminal of thethird capacitor 123 is electrically isolated from the second terminal ofthe fourth capacitor 124.

A first terminal of a third switch 141 is electrically connected to thenode 11, and a second terminal of the third switch 141 is electricallyconnected to the node 14. In some embodiments, the third switch 141 iscontrollable by an electrical signal. In some embodiments, the thirdswitch 141 is an N-type metal-oxide semiconductor (NMOS) transistor, aP-type metal-oxide-semiconductor (PMOS) transistor, a pass gate, or thelike. When the third switch 141 is closed (turned on, short-circuited),the second terminal of the first capacitor 121 is electrically connectedto the second terminal of the fourth capacitor 124. When the thirdswitch 141 is open (turned off, open-circuited), the second terminal ofthe first capacitor 121 is electrically isolated from the secondterminal of the fourth capacitor 124.

A first terminal of a fourth switch 142 is electrically connected to thenode 12, and a second terminal of the fourth switch 142 is electricallyconnected to the node 14. In some embodiments, the fourth switch 142 iscontrollable by an electrical signal. In some embodiments, the fourthswitch 142 is an N-type metal-oxide semiconductor (NMOS) transistor, aP-type metal-oxide-semiconductor (PMOS) transistor, a pass gate, or thelike. When the fourth switch 142 is closed (turned on, short-circuited),the second terminal of the third capacitor 123 is electrically connectedto the second terminal of the second capacitor 122. When the fourthswitch 142 is open (turned off, open-circuited), the second terminal ofthe third capacitor 123 is electrically isolated from the secondterminal of the second capacitor 122.

In some embodiments, the first capacitor 121, the second capacitor 122,the third capacitor 123, and the fourth capacitor 124 are integratedcapacitors, such as metal-oxide-metal (MOM) capacitors,metal-insulator-metal (MIM) capacitors, polysilicon capacitors, or thelike.

FIG. 4 is a diagram of the variable capacitor 311 having the firstcapacitance in accordance with various embodiments of the presentdisclosure. FIG. 5 is a diagram of the variable capacitor 311 having thesecond capacitance in accordance with various embodiments of the presentdisclosure. In FIG. 4, the first switch 131 is closed, the second switch132 is closed, the third switch 141 is open, and the fourth switch 142is open. In this configuration, the capacitance C₃₁₁ of the variablecapacitor 311 is given by the following formula:

$\begin{matrix}{C_{311} = {\frac{C_{A}}{2} + \frac{C_{B}}{2}}} & (1)\end{matrix}$

where C_(A) is capacitance of the first capacitor 121 and capacitance ofthe second capacitor 122, and C_(B) is capacitance of the thirdcapacitor 123 and capacitance of the fourth capacitor 124.

In FIG. 5, the first switch 131 is open, the second switch 132 is open,the third switch 141 is closed, and the fourth switch 142 is closed. Inthis configuration, the capacitance C₃₁₁ of the variable capacitor 311is given by the following formula:

$\begin{matrix}{C_{311} = \frac{2C_{A}C_{B}}{C_{2} + C_{B}}} & (2)\end{matrix}$

Based on formula (1) and formula (2), the capacitance delta (ΔC) of thevariable capacitor 311 is given by the following formula:

$\begin{matrix}{{\Delta\; C} = \frac{( {C_{B} - C_{A}} )^{2}}{2( {C_{B} + C_{A}} )}} & (3)\end{matrix}$

Assuming C_(B) is n times C_(A), formula (3) can be rewritten in termsof n as:

$\begin{matrix}{{\Delta\; C} = {\frac{( {n - 1} )^{2}}{2( {n + 1} )}C_{A}}} & (4)\end{matrix}$

Using formula (4), it can be seen that for C_(A) of 1 fF and n of 1.2(C_(B)=1.2 fF), the capacitance delta ΔC is approximately 9.1 aF.

FIGS. 6 and 7 are diagrams of switch circuits 600, 700 in accordancewith various embodiments of the present disclosure. The switch circuit600 has inverted operation relative to the switch circuit 700. Forexample, when the switch circuit 600 is turned on, the switch circuit700 is turned off. In some embodiments, the switch circuit 600 is usedas the switches 131, 132 of the variable capacitor 311, and the switchcircuit 700 is used as the switches 141, 142 of the variable capacitor311. As such, nodes 61 and 62 may correspond to nodes 11 and 12 (ornodes 13 and 14), respectively. Nodes 71 and 72 may correspond to nodes11 and 14 (or nodes 13 and 12), respectively.

A switch control signal S6 controls turning on or turning off of theswitch circuit 600. A first inverter 151 of the switch circuit 600receives the switch control signal S6, and inverts the switch controlsignal S6 to output an inverted switch control signal at an outputterminal of the first inverter 151. A second inverter 152 receives theinverted switch control signal at an input terminal of the secondinverter 152, and inverts the inverted switch control signal to output asignal having the same logical polarity as the switch control signal S6at an output terminal of the second inverter 152. A switching transistor171 is an NMOS transistor in some embodiments, and has a gate electrodeelectrically connected to the output terminal of the first inverter 151for receiving the inverted switch control signal. A first resistor 161has a first terminal electrically connected to the output terminal ofthe second inverter 152. A second terminal of the first resistor 161 iselectrically connected to a source electrode of the switching transistor171 (e.g., at the node 61). A second resistor 162 has a first terminalelectrically connected to the output terminal of the second inverter152. A second terminal of the second resistor 162 is electricallyconnected to a drain electrode of the switching transistor 171 (e.g., atthe node 62). The first resistor 161 and the second resistor 162 act asalternating current (AC) chokes. In some embodiments, the first resistor161 has impedance much greater than drain-source resistance (R_(DS)) ofthe transistor 171. For example, resistance of the first resistor 161may be 10, 100, or 1000 times the drain-source resistance of thetransistor 171. In some embodiments, the second resistor 162 hasimpedance much greater than the drain-source resistance (R_(DS)) of thetransistor 171. For example, resistance of the second resistor 162 maybe 10, 100, or 1000 times the drain-source resistance of the transistor171. In some embodiments, the resistance of the first resistor 161 issubstantially the same as the resistance of the second resistor 162. Insome embodiments, an integrated inductor is used in place of, or inaddition to, the first resistor 161 or the second resistor 162. In someembodiments, the first resistor 161 and the second resistor 162 arepolysilicon resistors, titanium-nitride (TiN) resistors, or the like.

A switch control signal S7 controls turning on or turning off of theswitch circuit 700. A first inverter 153 of the switch circuit 700receives the switch control signal S7, and inverts the switch controlsignal S7 to output an inverted switch control signal at an outputterminal of the first inverter 153. A second inverter 154 receives theinverted switch control signal at an input terminal of the secondinverter 154, and inverts the inverted switch control signal to output asignal having the same logical polarity as the switch control signal S7at an output terminal of the second inverter 154. A switching transistor172 is a PMOS transistor in some embodiments, and has a gate electrodeelectrically connected to the output terminal of the first inverter 153for receiving the inverted switch control signal. A first resistor 163has a first terminal electrically connected to the output terminal ofthe second inverter 154. A second terminal of the first resistor 163 iselectrically connected to a source electrode of the switching transistor172 (e.g., at the node 71). A second resistor 164 has a first terminalelectrically connected to the output terminal of the second inverter154. A second terminal of the second resistor 164 is electricallyconnected to a drain electrode of the switching transistor 172 (e.g., atthe node 72). The first resistor 163 and the second resistor 164 act asalternating current (AC) chokes. In some embodiments, the first resistor163 has impedance much greater than drain-source resistance (R_(DS)) ofthe transistor 172. For example, resistance of the first resistor 163may be 10, 100, or 1000 times the drain-source resistance of thetransistor 172. In some embodiments, the second resistor 164 hasimpedance much greater than the drain-source resistance (R_(DS)) of thetransistor 172. For example, resistance of the second resistor 164 maybe 10, 100, or 1000 times the drain-source resistance of the transistor172. In some embodiments, the resistance of the first resistor 163 issubstantially the same as the resistance of the second resistor 164. Insome embodiments, an integrated inductor is used in place of, or inaddition to, the first resistor 163 or the second resistor 164. In someembodiments, the first resistor 163 and the second resistor 164 arepolysilicon resistors, titanium-nitride (TiN) resistors, or the like.

FIGS. 8, 9, 10 and 11 are diagrams of operating modes of the switchcircuits 600, 700 in accordance with various embodiments of the presentdisclosure. In some embodiments, the switch control signal S6 and theswitch control signal S7 are the same signal, or have the same logicalpolarity. As shown in FIG. 8, the switch control signals S6, S7 have thelogical polarity 0 (e.g., low voltage). As a result, the gate electrodeof the transistor 171 has the logical polarity 1 (e.g., high voltage),and the source and drain electrodes of the transistor 171 have thelogical polarity 0 (e.g., low voltage). Positive gate-source voltage(V_(GS)) of the transistor 171 turns on the transistor 171, electricallyconnecting the node 61 to the node 62 of the switch circuit 600. In theswitch circuit 700, the gate electrode of the transistor 172 has thelogical polarity 1 (e.g., high voltage) when the switch control signalS7 has the logical polarity 0 (e.g., low voltage). The source and drainelectrodes of the transistor 172 have the logical polarity 0 (e.g., lowvoltage). Negative source-gate voltage (V_(SG)) of the transistor 172turns off the transistor 172, electrically isolating the node 71 fromthe node 72 of the switch circuit 700.

As shown in FIG. 9, the switch control signals S6, S7 have the logicalpolarity 1 (e.g., high voltage). As a result, the gate electrode of thetransistor 171 has the logical polarity 0 (e.g., low voltage), and thesource and drain electrodes of the transistor 171 have the logicalpolarity 1 (e.g., high voltage). Negative gate-source voltage (V_(GS))of the transistor 171 turns off the transistor 171, electricallyisolating the node 61 from the node 62 of the switch circuit 600. In theswitch circuit 700, the gate electrode of the transistor 172 has thelogical polarity 0 (e.g., low voltage) when the switch control signal S7has the logical polarity 1 (e.g., high voltage). The source and drainelectrodes of the transistor 172 have the logical polarity 1 (e.g., highvoltage). Positive source-gate voltage (V_(SG)) of the transistor 172turns off the transistor 172, electrically connecting the node 71 to thenode 72 of the switch circuit 700.

In FIGS. 10 and 11, an NMOS transistor 173 is used in the switch circuit700 instead of the transistor 172 (PMOS) shown in FIG. 7. A gateelectrode of the NMOS transistor 173 is electrically connected to theoutput terminal of the first inverter 153. A source electrode of theNMOS transistor 173 is electrically connected to the node 71, and adrain electrode of the NMOS transistor 173 is electrically connected tothe node 72. In some embodiments, the transistors 171 and 173 are PMOStransistors. The transistors 171, 173 are of the same doping polarity(N-type, P-type). The transistors 171, 172 are of different dopingpolarities.

In FIG. 10, the switch control signal S7 has the logical polarity 1(e.g., high voltage) when the switch control signal S6 has the logicalpolarity 0 (e.g., low voltage). As a result, the gate electrode of thetransistor 171 has the logical polarity 1 (e.g., high voltage) due toinverting action of the first inverter 151, and the source and drainelectrodes of the transistor 171 have the logical polarity 0 (e.g., lowvoltage) due to the inverting action of the second inverter 152. Thetransistor 171 is turned on due to positive gate-source voltage (V_(GS))of the transistor 171, which electrically connects the node 61 to thenode 62 in the switch circuit 600. The switch control signal S7 has thelogical polarity 1 (e.g., high voltage). As a result, the gate electrodeof the NMOS transistor 173 has the logical polarity 0 (e.g., lowvoltage) due to inverting action of the first inverter 153, and thesource and drain electrodes of the NMOS transistor 173 have the logicalpolarity 1 (e.g., high voltage) due to the inverting action of thesecond inverter 154. The NMOS transistor 173 is turned off due tonegative gate-source voltage (V_(GS)) of the NMOS transistor 173, whichelectrically isolates the node 71 from the node 72 in the switch circuit700.

In FIG. 11, the switch control signal S7 has the logical polarity 0(e.g., low voltage) when the switch control signal S6 has the logicalpolarity 1 (e.g., high voltage). As a result, the gate electrode of thetransistor 171 has the logical polarity 0 (e.g., low voltage) due toinverting action of the first inverter 151, and the source and drainelectrodes of the transistor 171 have the logical polarity 1 (e.g., highvoltage) due to the inverting action of the second inverter 152. Thetransistor 171 is turned off due to negative gate-source voltage(V_(GS)) of the transistor 171, which electrically isolates the node 61from the node 62 in the switch circuit 600. The switch control signal S7has the logical polarity 0 (e.g., low voltage). As a result, the gateelectrode of the NMOS transistor 173 has the logical polarity 1 (e.g.,high voltage) due to inverting action of the first inverter 153, and thesource and drain electrodes of the NMOS transistor 173 have the logicalpolarity 0 (e.g., low voltage) due to the inverting action of the secondinverter 154. The NMOS transistor 173 is turned on due to positivegate-source voltage (V_(GS)) of the NMOS transistor 173, whichelectrically connects the node 71 to the node 72 in the switch circuit700.

FIG. 12 is a flowchart of a method 20 of operating an electronic devicewith switched-capacitor tuning in accordance with various embodiments ofthe present disclosure. In some embodiments, the method 20 operates theelectronic device 10. The following description of the method 20 is madewith reference to the electronic device 10 and the FIGS. 1-11 describedabove. In block 200, a first capacitor, such as the first capacitor 121,is provided. The first capacitor has a first terminal electricallyconnected to a first terminal of a third capacitor, such as the thirdcapacitor 123. In block 210, a second capacitor, such as the secondcapacitor 122, is provided. The second capacitor has a first terminalelectrically connected to a first terminal of a fourth capacitor, suchas the fourth capacitor 124.

In block 220, a first switch, such as the first switch 131, is turned onin a first period to electrically connect a second terminal of the firstcapacitor to a second terminal of the second capacitor. In block 230, asecond switch, such as the second switch 132, is turned on in the firstperiod to electrically connect a second terminal of the third capacitorto a second terminal of the fourth capacitor. In some embodiments,completion of the blocks 220 and 230 results in the variable capacitor311 configuration shown in FIG. 4. In some embodiments, the blocks 220and 230 are performed simultaneously.

In block 240, a third switch, such as the third switch 141, is turned onin a second period to electrically connect the second terminal of thefirst capacitor to the second terminal of the fourth capacitor. In block250, a fourth switch, such as the fourth switch 142, is turned on in thesecond period to electrically connect the second terminal of the thirdcapacitor to the second terminal of the second capacitor. In someembodiments, completion of the blocks 240 and 250 results in thevariable capacitor 311 configuration shown in FIG. 6. In someembodiments, the blocks 240 and 250 are performed simultaneously. Insome embodiments, the blocks 220 and 230 are performed by the switchcircuit 600 shown in FIG. 6, and the block 230 is performed by theswitch circuit 700 shown in FIG. 7. In some embodiments, the blocks 240and 250 are performed by the switch circuit 700 shown in FIG. 7.

In some embodiments, the block 220 further includes turning off thethird switch to electrically isolate the second terminal of the firstcapacitor from the second terminal of the fourth capacitor. In someembodiments, the block 230 further includes turning off the fourthswitch to electrically isolate the second terminal of the thirdcapacitor from the second terminal of the second capacitor.

In some embodiments, the block 240 further includes turning off thefirst switch to electrically isolate the second terminal of the firstcapacitor from the second terminal of the second capacitor. In someembodiments, the block 250 further includes turning off the secondswitch to electrically isolate the second terminal of the thirdcapacitor from the second terminal of the fourth capacitor.

FIG. 13 is a circuit diagram of a digitally-controlled oscillator (DCO)30 in accordance with various embodiments of the present disclosure. TheDCO 30 is operable over a range of frequencies from a minimum frequencyf_(min) to a maximum frequency f_(max). Transistors 321, 322 of the DCO30 are biased by a current source 340, and electrically connected to aresonant load including a capacitor bank 330 and inductors 301, 302 tiedto a voltage supply node VDD. In some embodiments, the transistors 321,322 are NMOS transistors.

A finite number of intermediate frequencies between the minimumfrequency f_(min) and the maximum frequency f_(max) are selectablethrough digital control of the capacitor bank 330 by a controller 350.The capacitor bank 330 has variable capacitance controllable by controlsignals 351, 352, 353, . . . , 354 of the controller 350. In someembodiments, when the control signals 351, 352, 353, . . . , 354outputted by the controller 350 to the capacitor bank 330 all have afirst logical polarity (e.g., logic 0, logic low), operating frequencyof the DCO 30 is the minimum frequency f_(min). In some embodiments,when the control signals 351, 352, 353, . . . , 354 all have a secondlogic polarity (e.g., logic 1, logic high), the operating frequency ofthe DCO 30 is the maximum frequency f_(max).

In some embodiments, each capacitor of capacitors 331, 332, 333, . . . ,334 is a variable capacitor similar to, or identical to, the variablecapacitor 311. Each capacitor of the capacitors 331, 332, 333, . . . ,334 is associated with a first capacitance (e.g., C₀ _(—) ₃₃₁, C₀ _(—)₃₃₂) and a second capacitance (e.g., C₁ _(—) ₃₃₁, C₁ _(—) ₃₃₂). Eachcapacitor of the capacitors 331, 332, 333, . . . , 334 is associatedwith a capacitance delta. For example, the capacitor 331 is associatedwith a capacitance delta equal to C₁ _(—) ₃₃₁-C₀ _(—) ₃₃₁. A unitcapacitance delta may be defined as ΔC. The capacitors 331, 332, 333, .. . , 334 of the capacitor bank 330 have the same or differentcapacitance values (or capacitance deltas). In some embodiments, a firstgroup of the capacitors 331, 332, 333, . . . , 334 have binary-codedcapacitance deltas (e.g., 16*ΔC, 8*ΔC, 4*ΔC), and a second group of thecapacitors 331, 332, 333, . . . , 334 have thermometer-coded capacitancedeltas (e.g., ΔC, ΔC, ΔC).

The capacitor bank 330 and inductors 301, 302 form a resonator whoseoscillation frequency is given by:

$\begin{matrix}{\omega_{osc} = \frac{1}{\sqrt{L \cdot ( {C_{\min} + {{n \cdot \Delta}\; C}} )}}} & (5)\end{matrix}$

where L is the sum of the inductances of the inductors 301 and 302,C_(min) is minimum (baseline) capacitance of the capacitor bank 330(e.g., C₀ _(—) ₃₃₁+C₀ _(—) ₃₃₂+ . . . +C₀ _(—) ₃₃₄), ΔC is the unitcapacitance delta, and n is a number from 0 to N, where N is number ofthe capacitors 331, 332, 333, . . . , 334 in the capacitor bank 330. Amaximum capacitance C_(max) of the capacitor bank 330 is, then, equal toC_(min)+N*ΔC.

In some embodiments, the controller 350 dynamically controls thecapacitance of the capacitor bank 330. In some embodiments, thecontroller 350 receives an input signal from an external circuit, andvaries the capacitance of the capacitor bank 330 based on the inputsignal. In some embodiments, the DCO 30 is in an all-digitalphase-locked loop (ADPLL), and the controller 350 receives a phase orfrequency error signal from a detector circuit of the ADPLL. The errorsignal indicates whether a clock signal outputted by the DCO 30 shouldbe sped up (increase oscillation frequency) or slowed down (decreaseoscillation frequency) to achieve a phase or frequency lock with anexternal clock signal. If the oscillation frequency of the DCO 30 is tobe increased, the controller 350 adjusts the control signals 351, 352,353, . . . , 354 to decrease the capacitance of the capacitor bank 330.If the oscillation frequency of the DCO 30 is to be decreased, thecontroller 350 adjusts the control signals 351, 352, 353, . . . , 354 toincrease the capacitance of the capacitor bank 330.

In some embodiments, the controller 350 statically controls thecapacitance of the capacitor bank 330. In some embodiments, thecapacitor bank 330 and the controller 350 are applied to a tunableamplifier instead of to the DCO 30. In a functional test phase ofdevelopment of an integrated circuit die including the tunableamplifier, a parameter of the tunable amplifier, such as gain,bandwidth, linearity or the like is characterized through testequipment. Based on the characterization, the controller 350 receives aprogramming signal for permanently setting logical polarities of thecontrol signals 351, 352, 353, . . . , 354. In some embodiments, a firstterminal of the capacitor bank 330 (e.g., the node 31 of FIG. 3) iselectrically connected to an input terminal of the tunable amplifier,and a second terminal of the capacitor bank 330 (e.g., the node 32 ofFIG. 3) is electrically connected to an output terminal of the tunableamplifier. In some embodiments, the controller 350 includes a bank offuses corresponding to the control signals 351, 352, 353, . . . , 354.To set the logical polarities, the fuses are selectively blown orpreserved to set the control signals 351, 352, 353, . . . , 354 to havelogic high or logic low polarities.

FIG. 14 is a flowchart of a method 40 of manufacturing an electronicdevice with switched-capacitor tuning in accordance with variousembodiments of the present disclosure. In some embodiments, the method40 manufactures an integrated circuit (IC) die including adigitally-controllable capacitor bank, such as the capacitor bank 330,and a controller, such as the controller 350. In some embodiments, themethod 40 is performed partially or fully in an electronic designautomation (EDA) environment run on a physical server. The physicalserver includes at least a processing unit and a memory unit. In block400, a minimum frequency and a maximum frequency of a resonatorincluding the capacitor bank are determined. In some embodiments, theminimum frequency and the maximum frequency are inputted to the physicalserver by a user through an input device, such as a mouse or a keyboard.In block 410, resolution of intermediate frequencies between the minimumand maximum frequencies is determined. In some embodiments, theresolution is a number of the intermediate frequencies. In someembodiments, the resolution is a frequency step or delta of theintermediate frequencies. In some embodiments, the user selects thenumber in a graphical user interface of the EDA environment, through adrop-down box, a radio button, or the like. In some embodiments, thefrequency step is calculated by the server according to the number.

In block 420, an inductor type and an inductance of an inductive element(e.g., an inductor) are set according to the minimum and maximumfrequencies and a quality factor (Q). In some embodiments, the inductortype is selected from a library of inductor models, and parameters of aninductor model are entered by the user to set the inductance and Q of aninductor. Examples of inductor types include planar spiral inductors,toroidal-meander type integrated (TMTI) inductors, solenoid-typeintegrated inductors (SI2's), or the like.

Variable capacitors of the capacitor bank, such as the variablecapacitor 311, have two capacitances alternately selected throughdigital control (e.g., a 1-bit control signal). First and secondcapacitances (e.g., minimum and maximum capacitances) of the variablecapacitors are determined in block 430 according to the minimum andmaximum frequencies, the resolution, and the inductance of the inductiveelement. In some embodiments, the block 430 is performed automaticallyby the server. For example, when the user enters values for the minimumfrequency, the maximum frequency, the number of intermediatefrequencies, and the inductance of the inductive element, the server maycalculate the first and second capacitances of the variable capacitorsassociated with the values entered. For example, a frequency range iscalculated by taking the difference of the maximum frequency and theminimum frequency, and the frequency range is further divided intointermediate frequencies according to the resolution. In someembodiments, the user further specifies coding type of the variablecapacitors. In some embodiments, the coding type is binary orthermometer. Based on the coding types, capacitance deltas associatedwith each of the variable capacitors are calculated.

In block 440, capacitances of first, second, third, and fourthcapacitors (e.g., the first capacitor 121, the second capacitor 122, thethird capacitor 123, and the fourth capacitor 124 of the variablecapacitor 311) are set. In some embodiments, the capacitances are setaccording to the resolution set in the block 410. For example, an i^(th)variable capacitor of the variable capacitors may be associated with acapacitive delta ΔC_(i), such that:

$\begin{matrix}{{\Delta\; C_{i}} = \frac{( {C_{B} - C_{A}} )^{2}}{2( {C_{A} + C_{B}} )}} & (6)\end{matrix}$

which is similar to the formula (3) above. In some embodiments, thecapacitance C_(A) of the first and second capacitors is set to acapacitance of an integrated capacitor having minimum feature size in asemiconductor process node (e.g., 65 nanometers, 40 nanometers, 28nanometers, or the like).

In block 450, the capacitances of the first, second, third, and fourthcapacitors of the variable capacitors of the capacitor block have beenset, and the inductance of the inductive element has been set. Usinglayout tools, a circuit layout including the resonator having thecapacitor block and the inductive element is generated. After the blocks400-440 are completed, the method provides for producing anon-transitory computer readable storage media with instructions forbuilding a mask set for the IC die based on the circuit layoutcontaining the resonator including the capacitor block and the inductiveelement.

Embodiments may achieve advantages. The capacitor block 330 using thevariable capacitor 311 is able to achieve high frequency resolution withlittle to no area penalty through use of the switched-capacitor networkshown in FIG. 3.

In accordance with various embodiments of the present disclosure, anelectronic device includes an inductive element, and at least onevariable capacitor. Each variable capacitor includes: a first capacitorhaving a first terminal electrically connected to a first terminal ofthe inductive element; a second capacitor having a first terminalelectrically connected to a second terminal of the inductive element; athird capacitor having a first terminal electrically connected to thefirst terminal of the inductive element; a fourth capacitor having afirst terminal electrically connected to the second terminal of theinductive element; a first switch circuit having a first terminalelectrically connected to a second terminal of the first capacitor, anda second terminal electrically connected to a second terminal of thesecond capacitor; a second switch circuit having a first terminalelectrically connected to a second terminal of the third capacitor, anda second terminal electrically connected to a second terminal of thefourth capacitor; a third switch circuit having a first terminalelectrically connected to the second terminal of the first capacitor,and a second terminal electrically connected to the second terminal ofthe fourth capacitor; and a fourth switch circuit having a firstterminal electrically connected to the second terminal of the secondcapacitor, and a second terminal electrically connected to the secondterminal of the second capacitor.

In accordance with various embodiments of the present disclosure, adigitally-controlled variable capacitor includes a first capacitorhaving a first terminal, a second capacitor having a first terminal, athird capacitor having a first terminal electrically connected to thefirst terminal of the first capacitor, and a fourth capacitor having afirst terminal electrically connected to the first terminal of thesecond capacitor. A first switch circuit has a first control terminal, afirst terminal electrically connected to a second terminal of the firstcapacitor, and a second terminal electrically connected to a secondterminal of the second capacitor. A second switch circuit has a secondcontrol terminal, a first terminal electrically connected to a secondterminal of the third capacitor, and a second terminal electricallyconnected to a second terminal of the fourth capacitor. A third switchcircuit has a third control terminal, a first terminal electricallyconnected to the second terminal of the first capacitor, and a secondterminal electrically connected to the second terminal of the fourthcapacitor. A fourth switch circuit has a fourth control terminal, afirst terminal electrically connected to the second terminal of thethird capacitor, and a second terminal electrically connected to thesecond terminal of the second capacitor. A controller has a first outputterminal electrically connected to the first control terminal, a secondoutput terminal electrically connected to the second control terminal, athird output terminal electrically connected to the third controlterminal, and a fourth output terminal electrically connected to thefourth control terminal.

In accordance with various embodiments of the present disclosure, amethod of operating an electronic device includes steps of: (a)providing a first capacitor having a first terminal electricallyconnected to a first terminal of a third capacitor; (b) providing asecond capacitor having a first terminal electrically connected to afirst terminal of a fourth capacitor; (c) switching a first switchcircuit to electrically connect a second terminal of the first capacitorto a second terminal of the second capacitor; (d) switching a secondswitch circuit to electrically connect a second terminal of the thirdcapacitor to a second terminal of the fourth capacitor while performingstep (c); (e) switching a third switch circuit to electrically connectthe second terminal of the first capacitor to the second terminal of thefourth capacitor; and (f) switching a fourth switch circuit toelectrically connect the second terminal of the third capacitor to thesecond terminal of the second capacitor while performing step (e).

Circuits are typically powered and/or biased by multiple voltages. Themultiple voltages set up potential differences that allow electricalcurrents to flow throughout the circuit to perform various functions.Typically, electrical currents are defined as flowing from high voltageto low voltage. Voltage sources in circuits are also often defined interms of a supply voltage and ground, with ground representing 0 Volts.Other definitions are sometimes given in terms of an upper supplyvoltage (VDD, VCC), and a lower supply voltage (VSS, VEE). Thus, acircuit that operates on a 1.8 Volt supply may be defined as having anupper bias of 0.9 Volts, and a lower bias of −0.9 Volts. In thefollowing description, the term “ground” should be interpreted asincluding low supply voltage, such as the −0.9 Volts in the previousexample, unless specifically referred to as “earth ground,” or the like.Voltage levels, being relative, are not then intended so much to limitthe scope of the disclosure, but more as a point of reference forconvenient illustration.

Metal-oxide-semiconductor (MOS) transistors are typically described interms of four transistor terminals: a gate, a source, a drain, and abulk. It should be appreciated that most MOS transistors are symmetricaldevices, such that the source and the drain thereof are interchangeable,and the terms “source” and “drain” often represent nomenclature forconvenience of discussion. Terminals of MOS transistors may also bereferred to as “electrodes,” “ends,” and the like, without anydistinction intended through use of these different names. Biasing ofsuch terminals is usually performed through direct or indirect contactbetween a direct current (DC) voltage source and the terminal beingbiased. The contact may be through metallization layers, contact vias,pads, bumps, and/or similar interconnect structures formed on and overdevice regions of the MOS transistors.

Moreover, “exemplary” is used herein to mean serving as an example,instance, illustration, etc., and not necessarily as advantageous. Asused in this application, “or” is intended to mean an inclusive “or”rather than an exclusive “or”. In addition, “a” and “an” as used in thisapplication are generally be construed to mean “one or more” unlessspecified otherwise or clear from context to be directed to a singularform. Also, at least one of A and B and/or the like generally means A orB or both A and B. Furthermore, to the extent that “includes”, “having”,“has”, “with”, or variants thereof are used in either the detaileddescription or the claims, such terms are intended to be inclusive in amanner similar to the term “comprising”.

Although the present embodiments and their advantages have beendescribed in detail, it should be understood that various changes,substitutions, and alterations can be made herein without departing fromthe spirit and scope of the disclosure as defined by the appendedclaims. Moreover, the scope of the present application is not intendedto be limited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods, and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the present disclosure.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps.

What is claimed is:
 1. An electronic device comprising: an inductiveelement; and at least one variable capacitor, each comprising: a firstcapacitor having a first terminal electrically connected to a firstterminal of the inductive element; a second capacitor having a firstterminal electrically connected to a second terminal of the inductiveelement; a third capacitor having a first terminal electricallyconnected to the first terminal of the inductive element; a fourthcapacitor having a first terminal electrically connected to the secondterminal of the inductive element; a first switch circuit having a firstterminal directly connected to a second terminal of the first capacitor,and a second terminal directly connected to a second terminal of thesecond capacitor; a second switch circuit having a first terminaldirectly connected to a second terminal of the third capacitor, and asecond terminal directly connected to a second terminal of the fourthcapacitor; a third switch circuit having a first terminal directlyconnected to the second terminal of the first capacitor, and a secondterminal directly connected to the second terminal of the fourthcapacitor; and a fourth switch circuit having a first terminal directlyconnected to the second terminal of the third capacitor, and a secondterminal directly connected to the second terminal of the secondcapacitor.
 2. The electronic device of claim 1, wherein: the firstswitch circuit comprises: a first transistor of a first type; a firstinverter having an output terminal electrically connected to a gateelectrode of the first transistor; a second inverter having an inputterminal electrically connected to the gate electrode of the firsttransistor; a first resistor having a first terminal electricallyconnected to an output terminal of the second inverter, and a secondterminal electrically connected to a drain electrode of the firsttransistor; and a second resistor having a first terminal electricallyconnected to the output terminal of the second inverter, and a secondterminal electrically connected to a source electrode of the firsttransistor; and the third switch circuit comprises: a second transistorof a second type opposite the first type; a third inverter having anoutput terminal electrically connected to a gate electrode of the secondtransistor; a fourth inverter having an input terminal electricallyconnected to the gate electrode of the second transistor; a thirdresistor having a first terminal electrically connected to an outputterminal of the fourth inverter, and a second terminal electricallyconnected to a drain electrode of the second transistor; and a fourthresistor having a first terminal electrically connected to the outputterminal of the fourth inverter, and a second terminal electricallyconnected to a source electrode of the second transistor.
 3. Theelectronic device of claim 1, wherein: the first switch circuitcomprises: a first transistor of a first type; a first inverter havingan output terminal electrically connected to a gate electrode of thefirst transistor; a second inverter having an input terminalelectrically connected to the gate electrode of the first transistor; afirst resistor having a first terminal electrically connected to anoutput terminal of the second inverter, and a second terminalelectrically connected to a drain electrode of the first transistor; anda second resistor having a first terminal electrically connected to theoutput terminal of the second inverter, and a second terminalelectrically connected to a source electrode of the first transistor;and the third switch circuit comprises: a second transistor of the firsttype; a third inverter having an output terminal electrically connectedto a gate electrode of the second transistor; a fourth inverter havingan input terminal electrically connected to the gate electrode of thesecond transistor; a third resistor having a first terminal electricallyconnected to an output terminal of the fourth inverter, and a secondterminal electrically connected to a drain electrode of the secondtransistor; and a fourth resistor having a first terminal electricallyconnected to the output terminal of the fourth inverter, and a secondterminal electrically connected to a source electrode of the secondtransistor.
 4. The electronic device of claim 1, further comprising: acurrent source; a first transistor having: a gate electrode electricallyconnected to the second terminal of the inductive element; a sourceelectrode electrically connected to the current source; and a drainelectrode electrically connected to the first terminal of the inductiveelement; and a second transistor having: a gate electrode electricallyconnected to the first terminal of the inductive element; a sourceelectrode electrically connected to the current source; and a drainelectrode electrically connected to the second terminal of the inductiveelement.
 5. The electronic device of claim 1, further comprising acontroller comprising at least one output terminal electricallyconnected to the at least one variable capacitor.
 6. The electronicdevice of claim 5, wherein the controller comprises an input terminalelectrically connected to a phase-locked loop.
 7. A digitally-controlledvariable capacitor comprising: a first capacitor having a firstterminal; a second capacitor having a first terminal; a third capacitorhaving a first terminal electrically connected to the first terminal ofthe first capacitor; a fourth capacitor having a first terminalelectrically connected to the first terminal of the second capacitor; afirst switch circuit having a first control terminal, a first terminalelectrically and operably connected to a second terminal of the firstcapacitor, and a second terminal electrically and operably connected toa second terminal of the second capacitor; a second switch circuithaving a second control terminal, a first terminal electrically andoperably connected to a second terminal of the third capacitor, and asecond terminal electrically and operably connected to a second terminalof the fourth capacitor; a third switch circuit having a third controlterminal, a first terminal electrically and operably connected to thesecond terminal of the first capacitor, and a second terminalelectrically and operably connected to the second terminal of the fourthcapacitor; a fourth switch circuit having a fourth control terminal, afirst terminal electrically and operably connected to the secondterminal of the third capacitor, and a second terminal electrically andoperably connected to the second terminal of the second capacitor; and acontroller having a first output terminal electrically connected to thefirst control terminal, a second output terminal electrically connectedto the second control terminal, a third output terminal electricallyconnected to the third control terminal, and a fourth output terminalelectrically connected to the fourth control terminal.
 8. Thedigitally-controlled variable capacitor of claim 7, wherein: the firstswitch circuit comprises: a first transistor of a first type; a firstinverter having an output terminal electrically connected to a gateelectrode of the first transistor; a second inverter having an inputterminal electrically connected to the gate electrode of the firsttransistor; a first resistor having a first terminal electricallyconnected to an output terminal of the second inverter, and a secondterminal electrically connected to a drain electrode of the firsttransistor; and a second resistor having a first terminal electricallyconnected to the output terminal of the second inverter, and a secondterminal electrically connected to a source electrode of the firsttransistor; and the third switch circuit comprises: a second transistorof a second type opposite the first type; a third inverter having anoutput terminal electrically connected to a gate electrode of the secondtransistor; a fourth inverter having an input terminal electricallyconnected to the gate electrode of the second transistor; a thirdresistor having a first terminal electrically connected to an outputterminal of the fourth inverter, and a second terminal electricallyconnected to a drain electrode of the second transistor; and a fourthresistor having a first terminal electrically connected to the outputterminal of the fourth inverter, and a second terminal electricallyconnected to a source electrode of the second transistor.
 9. Thedigitally-controlled variable capacitor of claim 7, wherein: the firstswitch circuit comprises: a first transistor of a first type; a firstinverter having an output terminal electrically connected to a gateelectrode of the first transistor; a second inverter having an inputterminal electrically connected to the gate electrode of the firsttransistor; a first resistor having a first terminal electricallyconnected to an output terminal of the second inverter, and a secondterminal electrically connected to a drain electrode of the firsttransistor; and a second resistor having a first terminal electricallyconnected to the output terminal of the second inverter, and a secondterminal electrically connected to a source electrode of the firsttransistor; and the third switch circuit comprises: a second transistorof the first type; a third inverter having an output terminalelectrically connected to a gate electrode of the second transistor; afourth inverter having an input terminal electrically connected to thegate electrode of the second transistor; a third resistor having a firstterminal electrically connected to an output terminal of the fourthinverter, and a second terminal electrically connected to a drainelectrode of the second transistor; and a fourth resistor having a firstterminal electrically connected to the output terminal of the fourthinverter, and a second terminal electrically connected to a sourceelectrode of the second transistor.
 10. The digitally-controlledvariable capacitor of claim 7, wherein the controller comprises a fuseelectrically connected to the first control terminal, the second controlterminal, the third control terminal, and the fourth control terminal.11. The digitally-controlled variable capacitor of claim 7, wherein thecontroller comprises an input terminal electrically connected to aphase-locked loop.
 12. The digitally-controlled variable capacitor ofclaim 7, wherein the first terminal of the first capacitor iselectrically connected to an input terminal of an amplifier, and thefirst terminal of the second capacitor is electrically connected to anoutput terminal of the amplifier.
 13. A method of operating anelectronic device, comprising steps of: (a) providing a first capacitorhaving a first terminal electrically connected to a first terminal of athird capacitor; (b) providing a second capacitor having a firstterminal electrically connected to a first terminal of a fourthcapacitor; (c) switching a first switch circuit to electrically andoperably connect a second terminal of the first capacitor to a secondterminal of the second capacitor; (d) switching a second switch circuitto electrically and operably connect a second terminal of the thirdcapacitor to a second terminal of the fourth capacitor while performingstep (c); (e) switching a third switch circuit to electrically andoperably connect the second terminal of the first capacitor to thesecond terminal of the fourth capacitor; and (f) switching a fourthswitch circuit to electrically and operably connect the second terminalof the third capacitor to the second terminal of the second capacitorwhile performing step (e).
 14. The method of claim 13, wherein: the step(c) comprises sending a first control signal to a first control terminalof the first switch circuit to turn on a first transistor of the firstswitch circuit; and the step (e) comprises sending the first controlsignal to a second control terminal of the second switch circuit to turnon a second transistor of the second switch circuit; wherein the firsttransistor and the second transistor are of different doping polarity;wherein the first control signal has a different logical polarity in thestep (c) than in the step (e).
 15. The method of claim 13, wherein: thestep (c) comprises sending a first control signal to a first controlterminal of the first switch circuit to turn on a first transistor ofthe first switch circuit; and the step (e) comprises sending a secondcontrol signal to a second control terminal of the second switch circuitto turn on a second transistor of the second switch circuit; wherein thefirst transistor and the second transistor are of the same dopingpolarity; wherein the first control signal has the same logical polarityin the step (c) as the second control signal has in the step (e). 16.The method of claim 13, wherein the first switch circuit has a firstcontrol terminal, the second switch circuit has a second controlterminal, the third switch circuit has a third control terminal, and thefourth switch circuit has a fourth control terminal, the method furthercomprising: (g) sending a first control signal having a first logicalpolarity to the first control terminal, the second control terminal, thethird control terminal and the fourth control terminal during the steps(c) and (d) by a controller; and (h) sending the first control signalhaving a second logical polarity different from the first logicalpolarity to the first control terminal, the second control terminal, thethird control terminal and the fourth control terminal during the steps(e) and (f) by the controller.
 17. The method of claim 13, furthercomprising: (i) receiving an error signal from a phase-locked loop by acontroller before the steps (c) and (d); wherein the steps (c) and (d)are performed by the controller in accordance with the error signal. 18.The method of claim 13, further comprising: (i) receiving an errorsignal from a phase-locked loop by a controller before the steps (e) and(f); wherein the steps (e) and (f) are performed by the controller inaccordance with the error signal.
 19. The method of claim 13, whereinthe first switch circuit has a first control terminal, the second switchcircuit has a second control terminal, the third switch circuit has athird control terminal, and the fourth switch circuit has a fourthcontrol terminal, wherein the steps (e) and (f) are performed by settinga fuse electrically connected to the first control terminal, the secondcontrol terminal, the third control terminal, and the fourth controlterminal.
 20. The method of claim 13, wherein the first switch circuithas a first control terminal, the second switch circuit has a secondcontrol terminal, the third switch circuit has a third control terminal,and the fourth switch circuit has a fourth control terminal, wherein thesteps (c) and (d) are performed by setting a fuse electrically connectedto the first control terminal, the second control terminal, the thirdcontrol terminal, and the fourth control terminal.